CODEWITHSUNDEEP
pythonpandas
swifty
swifty

Reputation: 1282

Make Multiple Shifted (Lagged) Columns in Pandas

I have a time-series DataFrame and I want to replicate each of my 200 features/columns as additional lagged features. So at the moment I have features at time t and want to create features at timestep t-1, t-2 and so on.

I know this is best done with df.shift() but I'm having trouble putting it altogether. I want to also rename the columns to 'feature (t-1)', 'feature (t-2)'.

My pseudo-code attempt would be something like:

lagged_values = [1,2,3,10]
for every lagged_values
    for every column, make a new feature column with df.shift(lagged_values)
    make new column have name 'original col name'+'(t-(lagged_values))'

In the end if I have 200 columns and 4 lagged timesteps I would have a new df with 1,000 features (200 each at t, t-1, t-2, t-3 and t-10).

I have found something similar but it doesn't keep the original column names (renames to var1, var2, etc) as per machine learning mastery. Unfortunately I don't understand it well enough to modify it to my problem.

def series_to_supervised(data, n_in=1, n_out=1, dropnan=True):
    """
    Frame a time series as a supervised learning dataset.
    Arguments:
        data: Sequence of observations as a list or NumPy array.
        n_in: Number of lag observations as input (X).
        n_out: Number of observations as output (y).
        dropnan: Boolean whether or not to drop rows with NaN values.
    Returns:
        Pandas DataFrame of series framed for supervised learning.
    """
    n_vars = 1 if type(data) is list else data.shape[1]
    df = DataFrame(data)
    cols, names = list(), list()
    # input sequence (t-n, ... t-1)
    for i in range(n_in, 0, -1):
        cols.append(df.shift(i))
        names += [('var%d(t-%d)' % (j+1, i)) for j in range(n_vars)]
    # forecast sequence (t, t+1, ... t+n)
    for i in range(0, n_out):
        cols.append(df.shift(-i))
        if i == 0:
            names += [('var%d(t)' % (j+1)) for j in range(n_vars)]
        else:
            names += [('var%d(t+%d)' % (j+1, i)) for j in range(n_vars)]
    # put it all together
    agg = concat(cols, axis=1)
    agg.columns = names
    # drop rows with NaN values
    if dropnan:
        agg.dropna(inplace=True)
    return agg

Upvotes: 12

Views: 11297

Answers (4)

David Gilbertson
David Gilbertson

Reputation: 4873

For those using the statsmodels package, there's a function called lagmat that does exactly this:

from statsmodels.tsa.tsatools import lagmat
df = lagmat(df, maxlag=3, use_pandas=True)

I don't think you can control the column names though, you'll get ColName.L.1, etc.

Docs: lagmat and lagmat2ds

Upvotes: 2

sammazerolle
sammazerolle

Reputation: 1

Its significantly faster to map across the lags and shift all columns at once. father than iterating through each lag / column..

from functools import partial

def addSimpleLags(df,lag_list,col_list,direction = 'lag'):

    if direction == 'lead':
        lag_list = map(lambda x: x*(-1),lag_list)

    arr_lags = list(map(partial(_buildLags,df=df,
                        col_list=col_list,
                        direction = direction),
                lag_list))

    df = pd.concat([df]+arr_lags,axis = 1)

    return df

def _buildLags(lag,df,col_list,direction):

    return df[col_list].shift(lag).add_suffix('_{}_{}'.format(np.abs(lag),direction))

Trying this out... ~5x faster than the accepted solution (for 5 lags x 261 cols x 3M rows)

Upvotes: 0

Cappo
Cappo

Reputation: 76

If you have a large data frame and rely on a substantial number of lagged values, you may want to apply a more efficient solution using pd.concat and pd.DataFrame.add_sufix:

df = pd.DataFrame(np.random.randn(5, 2), columns=list('AB'))    
lags = range(0, 3)

df = pd.concat([df.shift(t).add_suffix(f" (t-{t})") for t in lags], axis=1)  # add lags

Upvotes: 1

Alexander
Alexander

Reputation: 109626

You can create the additional columns using a dictionary comprehension and then add them to your dataframe via assign.

df = pd.DataFrame(np.random.randn(5, 2), columns=list('AB'))

lags = range(1, 3)  # Just two lags for demonstration.

>>> df.assign(**{
    f'{col} (t-{lag})': df[col].shift(lag)
    for lag in lags
    for col in df
})
          A         B   A (t-1)   A (t-2)   B (t-1)   B (t-2)
0 -0.773571  1.945746       NaN       NaN       NaN       NaN
1  1.375648  0.058043 -0.773571       NaN  1.945746       NaN
2  0.727642  1.802386  1.375648 -0.773571  0.058043  1.945746
3 -2.427135 -0.780636  0.727642  1.375648  1.802386  0.058043
4  1.542809 -0.620816 -2.427135  0.727642 -0.780636  1.802386

Upvotes: 31

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